CI helps releasing fast, it doesn't do anything about not stepping on each other's toes. You can imagine a case where two people are working on the same part of the codebase and having merge conflicts everywhere. CI doesn't help with that, though it does make it a little bit less stressful to resolve those conflicts.
Microservices forces boundaries, which in turn allows you to scale the number of teams to the number of service boundaries and now you're no longer stepping on each other.
With the disclaimer that I'm an embedded programmer so I don't have a dog in this fight, my reading of the literature suggests it's best seen as an organizational tool rather than a performance tool.
> In software engineering, continuous integration (CI) is the practice of merging all developers' working copies to a shared mainline several times a day. [1]
That certainly does help with avoiding conflicts. There are only so many conflicts that you can pick up in a few hours of work.
Microservices forces boundaries, which in turn allows you to scale the number of teams to the number of service boundaries and now you're no longer stepping on each other.
With the disclaimer that I'm an embedded programmer so I don't have a dog in this fight, my reading of the literature suggests it's best seen as an organizational tool rather than a performance tool.